/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.expression;

import java.util.List;

import org.springframework.lang.Nullable;

/**
 * Expressions are executed in an evaluation context. It is in this context that
 * references are resolved when encountered during expression evaluation.
 *
 * <p>There is a default implementation of this EvaluationContext interface:
 * {@link org.springframework.expression.spel.support.StandardEvaluationContext}
 * which can be extended, rather than having to implement everything manually.
 *
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 3.0
 */
public interface EvaluationContext {

    /**
     * Return the default root context object against which unqualified
     * properties/methods/etc should be resolved. This can be overridden
     * when evaluating an expression.
     */
    TypedValue getRootObject();

    /**
     * Return a list of accessors that will be asked in turn to read/write a property.
     */
    List<PropertyAccessor> getPropertyAccessors();

    /**
     * Return a list of resolvers that will be asked in turn to locate a constructor.
     */
    List<ConstructorResolver> getConstructorResolvers();

    /**
     * Return a list of resolvers that will be asked in turn to locate a method.
     */
    List<MethodResolver> getMethodResolvers();

    /**
     * Return a bean resolver that can look up beans by name.
     */
    @Nullable
    BeanResolver getBeanResolver();

    /**
     * Return a type locator that can be used to find types, either by short or
     * fully qualified name.
     */
    TypeLocator getTypeLocator();

    /**
     * Return a type converter that can convert (or coerce) a value from one type to another.
     */
    TypeConverter getTypeConverter();

    /**
     * Return a type comparator for comparing pairs of objects for equality.
     */
    TypeComparator getTypeComparator();

    /**
     * Return an operator overloader that may support mathematical operations
     * between more than the standard set of types.
     */
    OperatorOverloader getOperatorOverloader();

    /**
     * Set a named variable within this evaluation context to a specified value.
     *
     * @param name  variable to set
     * @param value value to be placed in the variable
     */
    void setVariable(String name, @Nullable Object value);

    /**
     * Look up a named variable within this evaluation context.
     *
     * @param name variable to lookup
     * @return the value of the variable, or {@code null} if not found
     */
    @Nullable
    Object lookupVariable(String name);

}
